Such a method and device is disclosed in U.S. Pat. No. 4,926,350, where information about fiber orientation is obtained using the feature of a wood surface that the dielectric constant is different over a wood surface along and across a fiber direction thereof. When a wood surface is introduced between a pair of capacitor plates, the wood becomes part of the resulting capacitor, the capacitance of which can be determined using a radio frequency signal. By changing the orientation of the capacitor plates, a maximum or minimum can be found, revealing the orientation of wood fibers at that location of the board.
This information can be used to detect knots or to estimate the strength of the board.
One issue associated with the above mentioned disclosure is how to further improve board evaluation, e.g. to provide an improved strength grading method.